Flame retardant particle board containing acidified borate and process for making the same



liltiwltiielii UIIIECG DH 3 321,421 FLAME RETARoANi PARTICLE BOARD CON-TAINING AClDlFlED BORATE AND PROCESS FOR MAKING THE SAME Antal (Anthony)Pataki, Shati U] Hossain, and William This invention relates to a methodfor making retardant particle board and to the product of such method.

Numerous flame-retardant chamicals, generally useful for theflame-retardant treatment of cellulosic and lignocellulosic materialsare described in the literature, among which boric acid, sodiumtetraborate, ammonium sulphate, ammonium sulphamate, ammoniumphosphates, zinc chloride or their combinations, are perhaps the bestknown.

None of the chemicals commonly used for imparting flame retardance toligno-cellulosic materials are entirely satisfactory for use in thefield of particle board, as no suitable means compatibile with theprocess of particle board manufacture have been devised for theapplication of these chemicals.

In accordance with this invention it has been found that an aqueoussolution of an alkali metal borate acidified with an inorganic acidprovides a chemical system which permits the flame retardant treatmentto be an integral part of the particle board manufacturing process.Alkaline earth metal borates may be used in substitution for part or allof the alkali metal borate.

The methods used for preparing flame-retardant particle boards inaccordance with the present invention will be illustrated by theexamples below. In these experiments, laboratory particle boards wereprepared .from wood l me delphia, U.S.

led May 23, 1967 EXAMPLE I A batch of 3320 g. of poplar aspen flakes wasplaced in a mechanical mixer. An aqueous solution, containing 65 g. ofhydrochloric acid and 255 g. of sodium tetraflakes made from poplaraspen logs by means of a mechanical flaker. The flakes had a moisturecontent of 5% The synthetic resin used for the preparation of the boardswas of the urea-formaldehyde type containing 60% resin solids (MonsantoUF-1014, manufactured by the Monsanto Chemical Company, Montreal,Quebec, Canada). The resin was used in an amount of 7% solids, based onthe weight of the final board. The catalyst used was ammonium hydroxide,ammonium sulphate and water, in a ratio of 4:2:4 (by weight). Molten wax(Light Plasticrude, manufactured by the National Wax Company, Skokie,111., U.S.), in an amount of 2% of the weight of the board, was used inconjunction with the synthetic resin binder.

The flame-retardant properties of the particle board prepared inaccordance with the examples described below were evaluated bysubmitting the boards to a modified version of the Schyler test with thefollowing procedure being used.

Two specimen panels (9" x 30") were placed vertically in a suitablemetal frame, with the surfaces to be tested held parallel and facingeach other. The distance between the surfaces was two inches, and thebottom edge of one panel was situated four inches above the bottom edgeof the other, for proper draught. A Bunsen burner titted with a wing-tipand attached to a propane gas supply was used for the igniting flame.The burner was adjusted to produce yellow flame and the gas flow wasadjusted to approximately 2 cu. ft./hr. The ignition period was 10 min.

The height of the flame on the test panels was reduced borate (both onan anhydrous basis) in 1190 g. of water, at a temperature of C., wassprayed onto the flakes. The flame-retardant composition 'had the mol.ratio (mole hydrochloric acidzmole sodium tetraborate) of 1.3, and thesolution had a pH of 5.8, taken at a temperature of 75 C. The wet flakeswere dried to 5% moisture con tent, at about 250 F. in a forced-airdryer. The dry flakes were then sprayed with 468 g. of the liquidsynthetic resin, along with 26.5 g. of catalyst and g. of molten wax.One board (22" x 24" x A") was made with the aforementioned furnish, bypressing in a steam heated hydraulic press. The press temperature was300 F., initial pressure was 300 p.s.i., which was reduced to p.s.i. ata specified time during pressing. Total press time was 7 min. Thefinished boards were then conditioned for testing at 50% RH. at 73 F.

EXAMPLE II A batch of 3160 g. of flakes was treated according to theprocedure outlined above, with 2000 g. of a flameretardant compositioncontaining 164 g. of anhydrous phosphoric acid and 276 g. of anhydroussodium tetraborate. The flame-retardant composition had a mol. ratio(phosphoric acidzsodium tetraborate) of 1.2, and the solution had a pHof 5.8, taken at a temperature of 75 C. The treated flakes were furtherprocessed in accordance with the steps outlined in Example 1.

EXAMPLE III A batch of 3160 g. of flakes was treated according to theprocedure outlined in Example I, with 1830 g. of a flame-retardantcomposition containing 152 g. of nitric acid and 288 g. of sodiumtetraborate, on an anhydrous basis. The flame-retardant composition hada mol ratio (nitric acid:sodium tetraborate, on an anhydrous basis. Theflame-retardant composition had a mol. ratio (nitric acid: sodiumtetraborate) of 1.7, and the solution had a pH of 6.3, taken at atemperature of 75 C. The flakes were further processed in accordancewith the steps outlined in Example I; except, that 3 16 in. boards weremade from this furnish, and the pressing time was shortened to 3 /2min., which is generally used for the pressing of boards of 7 in.thickness.

EXAMPLE IV A batch of 3120 g. of flakes was treated according to theprocedure outlined in Example I, with 1460 g. of a flame-retardantcomposition containing g. of hydrochloric acid and 530 g. of sodiummetaborate, both on an anhydrous basis. The flame-retardant compositionhad :1 mol. ratio (hydrochloric acid:sodium metaborate) of 1.6, and thesolution had a pH of 5.8, taken at a temperature of 75 C. The flakeswere then processed in accordance with the steps outlined in Example I.

The results which appear in Tables 1, 2 and 3 will be discussedseparately.

' Table l The data in this table clearly establish the fact that thechemical system comprising an alkali metal borate acidified with aninorganic acid, is a very effective agent for conferring flameretardance on particle boards. It

will be seen from the table that the untreated board had.

a flamespread in excess of 50 inches, whereas the treated ones showedmuch lower values. The table shows data on four systems; hydrochloricacid-sodium tetraborate, phosphoric acid-sodium tetraborate, nitricacid-sodium tetra borate, and hydrochloric acid-sodium metaborate, allof which fall under the general classification of alkali metal boratesacidified with inorganic acids. in ancillary factors, such as the totalchemical concentration (which was varied between l2 and 33%), and theWide variations acidzalkali metal borate mol. ratio (which was variedbetween 1.3-1.7), the actual amount of flame-retardant chemicalsretained by the final board. (ranging from 7- 12%) are included in thetable, to show the general flexibility of the chemical system. I

Table II The data in Table II show an inverse relationship be- I tweenthe solution concentration of the acidified alkali metal borate,represented here by hydrochloric acid-sodium tetraborate, and theflamespread values. The data have been aranged into three groups: thefirst with 4% flameretardant chemicals in the finished board, the secondand third with about 8% and 11% respectively.

It may be seen that the flame reta-rdance of the finished Table III Theexamples in this table demonstrate the relationship between theacid-alkali metal borate mol. ratio and the physical strength propertiesof the flame-retardant particle board. The perpendicular tensilestrength (henceforth P.T.S.) was chosen to illustrate the strengthproperties.

Table III shows that a very definite high peak in the P.T.S. valuesappears at mol. ratios characteristic of each individual acidifiedborate system. This peak appears at a hydrochloric acid-sodiumtetraborate mol. ratio range of 1.0 to 1.5, at a hydrochloricacid-sodium metaborate mol. ratio range of 1.6-1.8, and at a phosphoricacidsodium tetraborate mol. ratio range of 0.8 to 1.2. Outside theseacid alkali metal borate mol. ratio ranges the hoard from wood flakesthe step of applying to such flakes a solution consisting essentially ofan aqueous solution of a borate selected from the groups consisting ofalkali and alkaline earth metal borates acidified with an inorganicacid, the mol ratio of acid to borate being between 0.5 and 2.5.

2. A process as in claim 1 in which the borate is sodium tetraborate.

3. A process as in claim 1 in which the borate is sodium metaborate.

4. A process as in claim 1 in which the inorganic acid is selected fromthe group consisting of hydrochloric acid, phosphoric acid and nitricacid.

5. A process as in claim 1, in which the solution has a total chemicalconcentration of less than 40%.

6. A process as in claim 1, in which the total chemical concentration iswithin the range of 6 to 25%.

7. A process as in claim 1, in which the pH of the solution is between4.5 and 8. v 8. In a method for making fire retardant particle boardfrom wood flakes the step of applying to such flakes a solutionconsisting essentially of an aqueous solution of sodium tetraborateacidified with hydrochloric acid and having a mol. ratio range of 1 to1.5.

9. In a method for making fire-retardant particle board from wood flakesthe step of applying to such flakes a solution consisting essentially ofan aqueous solution of sodium metaborate acidified with hydrochloricacid and having a mol. ratio range of 1.6 to 1.8.

10. In a method for making fire-retardant particle board from woodflakes the step of applying to such flakes a solu tion consistingessentially of an aqueous solution of sodium tetraborate acidified withphosphoric acid and having a mol. ratio range of 0.8 to 1.2.

11. A method as in claim 8, in which the total chemical concentration iswithin the range of 6 to 25%. i 12. A flame retardant particle boardcomprising particles coated with a composition consisting essentially ofa borate selected from the group consisting of alkali and alkaline earthmetal borates acidified with an inorganic acid the mol ratio of acid toborate being 0.5 to 2.5, and a synthetic resin binder.

Referee :es Cited by the Examiner UNITED STATES PATENTS 1,396,26411/1921 Di Filippo ll7--l47 1,507,275 9/ 1924 Duify ll7-l00 1,942,9771/1934- Payne 117-133 WILLIAM D. MARTIN, Primary Examiner.

T. G. DAVIS, Assistant Examiner.

12. FLAME RETARDANT PARTICLE BOARD COMPRISING PARTICLES COATED WITH ACOMPOSITION CONSISTING ESSENTIALLY OF A BORATE SELECTED FROM THE GROUPCONSISTING OF ALKALI AND ALKALINE EARTH METAL BORATES ACIDIFIED WITH ANINORGANIC ACID THE MOL RATIO OF ACID TO BORATE BEING 0.5 TO 2.5, AND ASYNTHETIC RESIN BINDER.